An electric dipole antenna is capable of generating electromagnetic (EM) waves. A dipole antenna can consist of a piece of open wire which carries current. The current in an antenna oscillates at the frequency of transmission. A Hertzian dipole is a type of electric dipole that has a length much smaller than the wavelength of radiation.
Low frequency radio propagation can be used to reduce the effects (e.g. absorption) of structures (e.g. walls) on radio communications. To provide higher signal strength for lower frequency radio propagation, an antenna can be configured with increased length (e.g. 40 m for a ¼ wave monopole antenna at 1.8 MHz). Such a length inhibits portable operation (e.g. by one person in an urban environment) of a low frequency antenna system. Reducing the size of the antenna can lower the radiation resistance and efficiency. For example, a 1 m monopole antenna can have a radiation resistance of approximately 0.01 Ohm and an efficiency of approximately 0.01%.